This invention relates generally to the cable forming art, and more particularly to a method and apparatus for producing electrically conductive multi-conductor, non-metallic (NM) sheath cable from AWG 10, 12, and 14 copper and aluminum wire at speeds in excess of 750 feet per minute.
In U.S. Pat. No. 3,852,875, issued to K. W. Mc Amis and L. K. Brewton, and assigned to the assignee of this invention, there is disclosed a continuous system for the high-speed production of single strand insulated electrical wire, typically termed "T-wire." The aforementioned patent teaches a method and apparatus that is capable of producing Nos. 10, 12 and 14 AWG size plastic coated wire from 5/16 inch copper rod, and Nos. 10 and 12 AWG size plastic coated wire from 3/8 inch aluminum and aluminum alloy rod, in a continuous operation at wire speeds in excess of 2500 feet per minute. The rod is drawn down into wire by combined drawing and annealing apparatus, and then conveyed directly to an in-line extruder where it is covered with the plastic coating. The coated T-wire is cooled in a three-stage system including a cooling mist, a cooling spray, and a cooling bath. The wire exiting the continuous system was then coiled and stored for further processing.
The T-wire manufactured according to the method and apparatus of the aforementioned patent is typically utilized in the manufacture of NM cable of the type disclosed in U.S. Pat. No. 3,600,500, also assigned to the assignee of this invention. Such cable includes two insulated single strand conductors, a bare ground wire having a separation film wrapped thereabout for separating the same from the insulation of the conductor wires according to UL requirements, and a non-conductive filter material for strengthening purposes. The various wires and fillers are then jacketed with a PVC compound coating composition for insulation purposes.
Heretofore, when it was desired to manufacture NM type sheath cable, conventional stem packs containing the T-wire and bare conductor wire were transported by means of fork trucks to the location in the plant where the cable jacketing lines were located and arranged in a convenient manner such that the wires could be payed-out therefrom and brought together at the beginning of the jacketing lines for entry into the PVC compound extruder. Stem packs containing the insulated T-wire were simply transported as produced in the aformentioned tandem lines and temporarily stored in a relatively random manner on the floor of the plant in the region of the jacketing lines until they could be moved into position for subsequent pay-out and jacketing.
As should be apparent, this conventional system of material handling led to several difficulties. First of all, transportation of the stem packs by means of fork trucks often damaged the stem packs as well as the wire contained therein. Moreover, such a method of transportation was time-consuming and did not lend itself to continuous, high-speed processing methods. Moreover, materials control was rendered difficult by the random on-floor storage, and much time was lost in moving and re-positioning the stem packs to gain access to the desired lot of material. Specifically, since each jacketing line, of which several would be in operation simultaneously, requires the delivery of black-insulated and white-insulated T-wire (to identify the positive and negative conductors), as well as a bare ground wire thereto, much rearrangement and repositioning of the various stem packs having the requisite material contained therein had to be accomplished in order to pay-out the proper mix of wires to each of the jacketing lines.
It should be apparent that the above-described system could not readily lend itself to continuous high-speed operation, was cumbersome and wasteful of floor space, and rendered accurate inventory of materials extremely difficult.